import math
a,b,c,d=(float(x) for x in input().split())

l=(math.sqrt((a-c)*(a-c)+(b-d)*(b-d)))

print('{:.08f}'.format(l)) import math math float(x) for x in input().split() for x in input().split() x input().split() ().split () input split for x in input().split() float(x) float x a,b,c,d=(float(x) for x in input().split()) a (float(x) for x in input().split()) b c d l=(math.sqrt((a-c)*(a-c)+(b-d)*(b-d))) l math.sqrt((a-c)*(a-c)+(b-d)*(b-d)) math.sqrt math sqrt (a-c)*(a-c)+(b-d)*(b-d) (a-c)*(a-c) a-c a c a-c a c (b-d)*(b-d) b-d b d b-d b d print('{:.08f}'.format(l)) print '{:.08f}'.format(l) '{:.08f}'.format '{:.08f}' format l c,d=(float(x) for x in input().split()) (float(x) for x in input().split()) c d=(float(x) for x in input().split()) (float(x) for x in input().split()) d l=(math.sqrt((a-c)*(a-c)+(b-d)*(b-d))) math.sqrt((a-c)*(a-c)+(b-d)*(b-d)) l a,b,c,d=(float(x) for x in input().split()) (float(x) for x in input().split()) a b,c,d=(float(x) for x in input().split()) (float(x) for x in input().split()) b
import math
a,b,c,d=(float(x) for x in input().split())

l=(math.sqrt((a-c)*(a-c)+(b-d)*(b-d)))

print('{:.08f}'.format(l))
